Essential Questions
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How are minerals defined?
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How do minerals form?
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How are minerals classified?
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What is a mineral?
Vocabulary
Review
New
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element
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mineral
crystal
luster
hardness
cleavage
fracture
streak
specific gravity
What is a mineral?
Mineral Characteristics
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Earth’s crust is composed of about 3000 different minerals that play
important roles in forming rocks and in shaping Earth’s surface.
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A mineral is a naturally occurring, inorganic solid, with a specific
chemical composition and a definite crystalline structure.
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What is a mineral?
Mineral Characteristics
Naturally occurring and inorganic
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Minerals are naturally occurring, meaning that they are formed by natural
processes.
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All minerals are inorganic: they are not made from living organisms.
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What is a mineral?
Mineral Characteristics
Definite crystalline structure
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The atoms in minerals are arranged in regular, repeated, geometric patterns
that result in the formation of a crystal.
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A crystal is a solid in which the atoms are arranged in repeating patterns.
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What is a mineral?
Mineral Characteristics
Solids with specific compositions
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Minerals are solids and therefore have definite shapes and volumes.
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Each type of mineral has a chemical composition unique to that mineral.
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A few minerals are composed of single elements; however, the majority
are made from compounds.
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In some minerals, such as varieties of feldspar, chemical composition
can vary within a certain range, depending on the temperature at which
the mineral crystallizes.
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What is a mineral?
Rock-Forming Minerals
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Eight to ten of the 30 most common minerals are referred to as rock-forming
minerals because they make up most of the rocks in Earth’s crust.
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Rock-forming minerals are primarily composed of the eight most common
elements in Earth’s crust.
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What is a mineral?
Rock-Forming Minerals
Minerals from magma
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Molten material that forms and accumulates below Earth’s surface is called
magma.
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Magma is less dense than the surrounding solid rock, so it can rise upward
into the cooler layers of Earth’s interior, where it cools and crystallizes.
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What is a mineral?
Rock-Forming Minerals
Minerals from magma
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The type and number of elements in the magma determine which minerals
will form.
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The rate at which the magma cools determines the size of the mineral
crystals. Small crystals form from rapidly cooling magma, and large crystals
form from slowly cooling magma.
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What is a mineral?
Rock-Forming Minerals
Minerals from solutions
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A liquid is saturated when it becomes full of a dissolved substance and can
dissolve no more of that substance.
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If more of the substance is added to a saturated solution, it is called
supersaturated, and mineral crystals form into solids from the solution.
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Minerals that form from the evaporation of the liquid in which they were
dissolved are called evaporites.
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What is a mineral?
Identifying Minerals
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Geologists identify minerals using tests based on a mineral’s physical and
chemical properties: crystal form, luster, hardness, cleavage, fracture, streak,
color, specific gravity, texture, density, and special properties.
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What is a mineral?
Identifying Minerals
Crystal form
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Some minerals form such distinct crystal shapes that they are immediately
recognizable.
•
However, perfect crystals are not always formed, so identification based only
on crystal form is rare.
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What is a mineral?
Identifying Minerals
Luster
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The way that a mineral reflects light from its surface is called luster.
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There are two types of luster—metallic luster and nonmetallic luster.
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Luster should usually be used in combination with other physical
characteristics to identify a mineral.
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What is a mineral?
Identifying Minerals
Hardness
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Hardness is a measure of how easily a mineral can be scratched.
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German geologist Friedrich Mohs developed a scale by which an unknown
mineral’s hardness can be compared to the known hardness of ten easily
recognized minerals that, with the exception of diamond, are readily found in
nature.
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What is a mineral?
Identifying Minerals
Cleavage and fracture
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A mineral that splits relatively easily and evenly along one or more planes of
weak atomic bonds is said to have cleavage.
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To identify a mineral based on its cleavage, geologists count the number of
cleaved planes and study the angle or angles between them.
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Minerals that break with rough, arclike, or jagged edges because of their
tightly bonded atoms are said to have fracture.
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What is a mineral?
Identifying Minerals
Streak
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Streak is the color of a mineral when it is broken up and powdered.
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The streak test, which typically involves rubbing the mineral against an
unglazed porcelain plate, is most useful in identifying metallic minerals. It can
be used only on minerals that are softer than the porcelain plate.
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What is a mineral?
Identifying Minerals
Color
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Color is one of the most noticeable characteristics of a mineral.
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It is also one of the least reliable clues of a mineral’s identity.
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What is a mineral?
Identifying Minerals
Special properties
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Several special properties of minerals can also be used for identification
purposes. Some of these properties are magnetism, iridescence, double
refraction, effervescence with hydrochloric acid, and fluorescence.
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What is a mineral?
Identifying Minerals
Texture
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Texture describes how a mineral feels to the touch, and, like luster, it is
subjective. It is often used in combination with other tests to identify a
mineral.
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What is a mineral?
Identifying Minerals
Density and specific gravity
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Two minerals of the same size may have different weights due to a
difference in density.
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Density reflects the atomic mass and structure of a mineral.
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What is a mineral?
Identifying Minerals
Density and specific gravity
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𝑀
Density is expressed as D =
𝑉
where D = density, M = mass, and V = volume.
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Because density is not dependent on the size or shape of a mineral, it is a
useful identification tool.
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What is a mineral?
Identifying Minerals
Density and specific gravity
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The most common measure of density used by geologists is specific
gravity, the ratio of the mass of a substance to the mass of an equal
volume of water at 4°C.
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What is a mineral?
Review
Essential Questions
•
How are minerals defined?
•
How do minerals form?
•
How are minerals classified?
Vocabulary
• mineral
• crystal
• luster
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• hardness
• cleavage
• fracture
• streak
• specific gravity
What is a mineral?